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<br />42 <br /> <br />TECHNICAL MANUAL <br /> <br />Southern Plateau Region <br /> <br />The Southern Plateau Region comprises the southwestern part of Colorado <br />west of the Mountain Region (fig. 2). North of the Gunnison River the bound- <br />ary coincides with a 1 ine along an elevation of 7,500 ft, including the main- <br />stem tributaries of the Colorado River westward to the Utah State line. The <br />boundary south of the Gunnison River fol lows drainage ~ivide~ to the Rio <br />Grande, then it fol lows the Rio Grande to the State line. The part of the <br />region south of the Gunnison River includes both the Plateau section of ex- <br />treme western Colorado and the high, rugged terrain of the San Juan Mountains. <br /> <br />Annual precipitation ranges from 8 inches in some areas along the western <br />border to 50 inches in the San Juan Mountains. High-intensity rainfall occurs <br />during the summer months with infrequent rain storms during September and <br />October producing large floods on streams in the highest parts of the region. <br />Most annual floods result from snowmelt runoff during the spring months, but <br />these floods are usually much smaller than the infrequent floods during Sep- <br />tember and October. <br /> <br />The regression equations relating flood characteristics to basin param- <br />eters for the Southern Plateau Region are listed in table 4 with the corre- <br />sponding standard error of estimate for each equation. The equations for the <br />lOa-year flood discharge and depth are depicted graphically In figures 9 and <br />10, respectively. <br />